Most Medicare Part D Plans’ Formularies Included Humira Biosimilars for 2025

Why OIG Did This Review

• Humira, a biologic drug used to treat autoimmune conditions such as rheumatoid arthritis, is one of the best‑selling prescription drugs in the world. In the United States, it has an annual list price of approximately $90,000. In 2022, it cost the Part D program and enrollees $5.4 billion before accounting for rebates and other price concessions.
• The launch of Humira biosimilars (which are highly similar to Humira, with no clinically meaningful differences) has been anticipated as an opportunity to lower biologic drug costs through competition. However, if Part D plans’ formularies restrict access to Humira biosimilars, competitive pressure—and its potential effects on lowering drug costs—may be limited.
• Previous OIG work found that many Part D formularies did not cover biosimilars available for other expensive biologic drugs. OIG also found that this lack of formulary coverage could limit wider biosimilar use and any potential savings for Medicare Part D.

What OIG Found

Part D plans’ formulary coverage of Humira biosimilars increased substantially between 2024 and 2025.

Nearly all Part D Prescription Drug Plans (PDPs) (96 percent), and 88 percent of Medicare Advantage Prescription Drug (MAPD) plans, covered at least 1 of the 10 available Humira biosimilars on their 2025 formulary—including some plans that covered Humira biosimilars only and not Humira. This represents substantial growth in formulary coverage from 2024, when only 65 percent of PDPs and 52 percent of MAPD plans covered at least one of Humira’s biosimilars. However, 1 percent of PDP enrollees and 10 percent of MAPD enrollees were in plans that covered Humira only in 2025, which in effect prevents these enrollees’ use of Humira biosimilars.

Almost none of the formularies that covered Humira and its biosimilars used preferential tier placement to encourage biosimilar use.

Ninety-nine percent of these formularies placed Humira and its biosimilars on the same cost sharing tier. Likewise, these formularies either applied or did not apply utilization management requirements (i.e., prior authorization or step therapy) to both Humira and covered biosimilars. This means that the formularies did not use such tools to encourage the use of biosimilars, nor to discourage their use.

What OIG Concludes

Most—but not all—Part D plans covered Humira biosimilars in 2025. This increase in coverage is a positive trend, as both the Medicare Payment Advisory Commission and the Federal Trade Commission have raised concerns about the anticompetitive effects of limited biosimilar formulary coverage. OIG previously recommended that CMS monitor biosimilar coverage on formularies to identify any concerning trends, such as exclusion of biosimilars from formularies or preferential treatment for reference products like Humira. In response, CMS assessed whether 2024 Part D formularies included available biosimilars in addition to their reference products. We encourage CMS to continue this formulary monitoring.